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Thread: 445nm diode info

  1. #41
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    Aha, interesting. I read somewhere that the Nichia would have a 14um ridge, and this would be consistent then. However this was a forum read as well, without source given, so I can't tell how well founded this statement was.

    The reason why one sometimes sees dots near threshold may not necessarily be due to several emitters but perhaps just reflects a particular mode pattern, who knows. It appears only for one of two diodes I tested so far.

    Of course one can estimate the emitter dimensions by considering the divergences of the axes. The datasheet says (assuming it is the same chip as for the Nichia NDB7352) that the ratio of the axes is like 4:1, which seems a bit low for a 14um ridge. The divergence ratio from the various pictures shown here appears larger, but this is confused by astigmatism - that is, the ratio changes with the distance, so this is pretty meaningless.

    I intend to do precise measurements to determine the astigmatism and then see whether the data are consistent with the NDB7352. This is anyway needed for proper collimation. I believe a good way to collimate would be to first have a standard collimator close to the diode, followed by a long-fl cylinder lens to correct the astigmatism, then followed by a prism pair to bring the axis ratio down.

  2. #42
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    Sounds good.

    And if anyone has a broken one that they can't measure, standing offer here to measure the dimensions on SEM/high quality microscope/whatever it takes.

  3. #43
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    Actually I found the article from which you took the picture, it is called "Supermodes in Broad Ridge (Al,In)GaN Laser Diodes". I can't post it due to copyright. But I think it more or less answers the questions, thanks for the hint! The described behavior fits exactly the observations.

    Here an excerpt from the abstract:

    "Broad area (Al,In)GaN laser diodes (LDs) are suitable for high optical output power in the near UV to blue spectral range. But for ridge widths larger than a few micrometers, the occurrence of filamentation is well known. We present experimental evidence that the single filaments tend to be phase-locked with defined phase offset and build up a so called supermode. Depending on driving current a coherent or incoherent superposition of different super- modes can be observed...."

    The filaments they talk about are the intensity fluctuations shown in the figure you attached. They indeed don't reflect multiple emitters but mode patterns. As observed, they differ from diode to diode, and people in need of a clean pattern, such as us holographers, may need to select the "better" diodes.

  4. #44
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    Yep, Osram has put out several good papers the last couple of years.

    Nice job finding it so fast, that was quick.

  5. #45
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    The multimode beam is caused by different sets of quantum wells lighting up at different tiimes and current. Near threshold these diodes are essentially single-mode to about 60mw, with one mode lighting up,at full power they are very very much multimode like an 808nm pump diode.

  6. #46
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    Quote Originally Posted by heruursciences View Post
    The multimode beam is caused by different sets of quantum wells lighting up at different tiimes and current. Near threshold these diodes are essentially single-mode to about 60mw, with one mode lighting up,at full power they are very very much multimode like an 808nm pump diode.

    What "different sets of quantum wells"? I don't understand what you're saying, where are these "different sets"?

  7. #47
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    Quote Originally Posted by heruursciences View Post
    The multimode beam is caused by different sets of quantum wells lighting up at different tiimes and current. Near threshold these diodes are essentially single-mode to about 60mw, with one mode lighting up,at full power they are very very much multimode like an 808nm pump diode.
    You state this like facts... is it what you believe or something you know, and if so, from where?

  8. #48
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    Krazer did longdurance test he reached 1.75 from a single diode:


    http://www.krazerlasers.com/lasers/

  9. #49
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    NOTE-
    Yes the laser produced 1.76W when run at 2A, however this current is NOT safe to run the diode at, it causes a steady, permanent degradation of the diode. On the bright side all of those tests were done with a stock lens, and with a with a high(er) quality lens one should expect a slight improvement.

  10. #50
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    Well I finally found some time to build a 445nm Laser that I got
    from EF... I installed it into an Aixiz Module using a 405 G-1 lens.
    It is mounted in a Z-Bolt clam shell heat sink..

    I did a bit of testing and here are my results...
    I tested in 100mW increments and stopped at 1300mW..
    I used an Opto Power Corporation OPC-PS4005 Laser
    Diode Driver.


    007mW ---- 220mA @ 3.95V Threshold
    050mW ---- 260mA
    100mW ---- 310mA @ 4.09V
    200mW ---- 380mA
    300mW ---- 460mA
    400mW ---- 540mA
    500mW ---- 620mA @ 4.46V
    600mW ---- 710mA
    700mW ---- 800mA
    800mW ---- 890mA
    900mW ---- 980mA
    1000mW -- 1090mA @ 4.79V
    1100mW -- 1210mA
    1200mW -- 1340mA
    1300mW -- 1530mA @ 4.99V


    For those of you that are trying to measure raw output
    on a thermal sensor without a lens... your readings will
    be skewed to a greater value...
    The reason for this is because the 445nm LD's case gets
    really hot and when you are very close to the sensor... the
    head reads the LD's heat radiation on top of the Laser's
    beam.. once you are a few inches away.. that effect is
    negligible...


    BTW... I found a 3/8" inside diameter rubber grommet that
    serves as a lens ring adjustment method to not burn my
    fingers.. It fits right over the knurled lens cap..
    It's cheap and it works...

    [EDIT]
    This was a test of the A130 LD

    Jerry
    Last edited by lasersbee; 06-29-2010 at 06:53.
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